Much work has been done in the field of gelatinous elastomers. U.S. Pat. No. 5,994,450 by inventor Tony M. Pearce, which is hereby incorporated by reference, discloses gelatinous elastomers (“gel”) made from a plasticizer or plasticizing fluid, such as mineral oil, and an A-B-A triblock copolymer, such as styrene-ethylene-ethylene-styrene (SEEPS). The copolymer is plasticized so that at least some of the plasticizer associates with the mid block B. An alternative A-B-A triblock copolymer is styrene-ethylene-butylene-styrene (SEBS) as taught in U.S. Pat. No. 4,369,284 by John Y. Chen, which is hereby incorporated by reference. Most makers of gelatinous elastomer materials and articles today express a strong preference for gels made with SEEPS rather than SEBS due to superior strength and elongation, reduced oil bleed, and other desirable material properties.
SEBS polymers are made by a number of suppliers, including SEPTON® Company of America in Pasadena, Tex. as well as its parent company, Kuraray in Japan. SEBS polymers are also available from KRATON® Polymers, Inc. of Houston, Tex. However, SEEPS polymers are made only by one supplier, SEPTON® Company of America in Pasadena, Tex., and its parent company in Japan. Thus it would be advantageous to have a SEBS polymer that had, in comparison to SEEPS, similar or better strength and elasticity properties, similar or better non-bleed properties, and similar or better other properties, in a gel.
Ordinarily, makers of this A-B-A tri-block copolymer strive to have a narrow range of molecular weight in a given polymer. Then, they offer a number of different polymers, each with its own range of molecular weights. If a user desires to have some of the properties of two or more different molecular weights, the user would mix two or more polymers together. However, in my use of such mixing, I have not found that the resultant gel is desirable.
For example, I have mixed SEPTON® 4055 (a high molecular weight “Mw” SEEPS polymer) with SEPTON® 4044 (a medium molecular weight SEEPS polymer) and SEPTON® 4033 (a low molecular weight SEEPS polymer), then heat-blended these together with mineral oil and cooled the mixture into a cohesive gel. This would be considered a trimodal gel because the molecular weights of the polymers are centered around 3 different points. While the resultant gel is easier to fill into molds because of its lower melt viscosity, the structural properties of the resultant mixed-polymer gel have been inferior to gels made with SEPTON® 4055, SEEPS polymer, alone (a unimodal gel). I believe that the low molecular weight polymers reach their maximum elongation before the medium and high molecular weight polymers, and fail before the other polymers become strained, thus drastically reducing tensile strength and elongation at failure of the gel. Therefore I concluded that merely mixing various molecular weights of SEEPS triblock copolymers did not yield a desirable gel.